1. Field of the Invention
The present invention relates to the apparatus and method for monitoring a plasma processing apparatus. In particular, it relates to the apparatus and method for monitoring a plasma processing apparatus that reduces the processing failure caused by an abnormal discharge.
2. Description of the Related Art
In semiconductor manufacturing processes, plasma processing apparatus are widely used for micromachining processes, such as etching, film deposition and ashing. In a process involving plasma processing, a process gas introduced into a vacuum chamber (reactor) is changed into a plasma by plasma generator means and the plasma is caused to react with a surface of a semiconductor wafer to implement micromachining, and a volatile reaction product is discharged, thereby accomplishing the predetermined process.
With such a plasma processing apparatus, if the apparatus is used for a long time, components which are in direct contact with the plasma, such as the inner wall of the reactor, the upper electrode or a ring disposed around the wafer, are worn by the action of ions from the plasma. As a result, the gap between components or holes provided in a component (holes for blowing out the process gas, for example) becomes larger than the original (design) size. Such a larger gap or holes may result in another plasma occurring in the defined space. This discharge is so-called an xe2x80x9cabnormal dischargexe2x80x9d. In other words, if the plasma processing apparatus is used for a long time, the xe2x80x9cabnormal dischargexe2x80x9d occurs therein.
In the past, abnormal discharge has been prevented from occurring by determining empirically a cumulative processing time from the replacement of a component to the occurrence of abnormal discharge, and replacing components with reference to this determined time. Japanese Patent Laid-Open No. 9-92491 entitled xe2x80x9cPLASMA PROCESSING APPARATUS AND PLASMA PROCESSING METHODxe2x80x9d discloses a technique of reducing the frequency of occurrence of the abnormal discharge by detecting an occurrence of the abnormal discharge in a plasma processing container by a change in the reflected wave of a high frequency power applied to the plasma or change in the plasma light emission, thereby suppressing unexpected particle occurrence caused by the abnormal discharge.
If the abnormal discharge occurs, a dissociation state of the process gas changes to deteriorate the etching capability thereof, or a reaction product film formed in the reactor is peeled off creating a foreign matter. Therefore, if components are worn and deteriorated causing abnormal discharge to occur, a normal etching can no longer be accomplished.
In the past, as described above, the cumulative processing time elapsed from the replacement of a component to the abnormal discharge occurrence was determined empirically, and whether or not to replace a component was determined with reference to the time. However, abnormal discharge sometimes occurs before the elapse of reference time for component replacement. In such a case, the occurrence of the abnormal discharge would be recognized when a failed wafer is found during inspection. Thus, by that time, a considerable amount of poorly processed wafers would have resulted.
Besides, according to the method described in the Japanese Patent Laid-Open No. 9-92491 described above, while the abnormal discharge occurring in the plasma can be detected, any abnormal discharge occurring with the inner portion of the gas hole of the upper electrode as described above cannot be detected.
Detecting the abnormal discharge substantially simultaneously with the occurrence thereof provides the following advantages. That is, consumable components, which have been replaced with reference to the cumulative processing time obtained empirically in the past, can be used until abnormal discharge actually occurs. Thus, the components can be used longer and the cost of the consumable components can be reduced. Furthermore, if the cumulative processing time until the occurrence of the abnormal discharge can be predicted, the replacement component can be prepared in advance, so that the replacement can be accomplished efficiently. In addition, since the etching can be stopped immediately after the occurrence of the abnormal discharge to take appropriate measures, the number of failed wafers can be reduced to one.
This invention has been devised in view of the points described above and provides an apparatus for monitoring a plasma processing apparatus that can predict the occurrence of an abnormal discharge and detect the occurrence thereof immediately.
In order to solve the problems described above, the present invention comprises the following means.
The present invention comprises a vacuum process chamber that contains an upper electrode having a conductive plate with gas supply holes for supplying a process gas and a lower electrode having a platform on which a sample is to be mounted; process gas supply means for supplying the process gas to the gas supply holes in the upper electrode and exhaust means for exhausting the vacuum process chamber; a high frequency power supply for applying a high frequency power to the upper electrode to generate a plasma between the upper and lower electrodes; a high frequency bias power supply for applying a high frequency power to the upper electrode to generate a direct current bias potential in the upper electrode; and abnormal discharge determination means for determining whether an abnormal discharge occurs or not based on the direct current bias potential generated in the upper electrode.